Method and system for a turbocharged engine

ABSTRACT

Methods and systems are provided for a boosted engine having a split intake system coupled to a split exhaust system. Aircharges of differing composition, pressure, and temperature may be delivered to the engine through the split intake system at different points of an engine cycle. In this way, boost and EGR benefits may be extended.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 12/878,838, entitled “Method and system forturbocharging an engine” filed Sep. 9, 2010, the disclosure of which ishereby incorporated by reference.

FIELD

The present description relates to a method for improving thermalefficiency of a turbocharged engine. The method may be particularlyuseful for providing EGR in a turbocharged engine.

BACKGROUND AND SUMMARY

In an effort to meet stringent federal government emissions standards,engine systems may be configured with exhaust gas recirculation (EGR)systems wherein at least a portion of the exhaust gas is recirculated tothe engine intake. Such EGR systems enable reduction in exhaustemissions while also improving fuel economy, especially at higher levelsof engine boost.

One example of such an EGR system is illustrated by Duret in U.S. Pat.No. 6,135,088. Therein, a first inlet port of the engine cylinder isconfigured to deliver EGR while a second inlet port is configured todeliver fresh air, boosted by a compressor, to the cylinder. In thisway, charge stratification can be achieved in the cylinder to improveself-ignition.

However, the inventors herein have recognized potential issues with sucha system. As one example, during some conditions, charge stratificationmay not be desired. Rather, charge homogenization may be desired toincrease engine performance and improve EGR benefits. As anotherexample, it may be difficult to maintain the charge stratification sinceboth inlet ports discharge exhaust gas through a common exhaust port. Asstill another example, the desired effects taught by Duret may be erasedif modified to use an exhaust turbine to drive the compressor.

Thus in one example, some of these issues may be at least partlyaddressed by a method of operating a boosted engine comprising, drawingat least some recirculated exhaust gas at or below barometric pressurefrom one of two exhaust passages into an engine cylinder through a firstintake passage, and drawing at least some fresh air at compressorpressure into the cylinder through a second, separate intake passagecoupled to the other of the two exhaust passages. In this way, freshboosted air may be delivered separate from the recirculated exhaust gas.The aircharges may then be mixed with each other and with fuel in thecylinder. The combined aircharge-fuel mixture may then be combusted inthe cylinder.

For example, an amount of exhaust gas (that is, low pressure EGR) may bedrawn from a first exhaust passage into a first intake passage through afirst EGR passage. The EGR may be naturally aspirated from the firstexhaust passage via a first exhaust valve and delivered to an enginecylinder at or below barometric pressure through a first intake valve ofthe first intake passage at a first, earlier intake valve timing. Forexample, the EGR may be delivered at the onset of an intake stroke. Atthe same time, an amount of fresh intake air may be drawn through aturbocharger compressor included in a second intake passage. As such,the second intake passage may be separate from the first intake passage,and the turbocharger may be coupled only to the second intake passageand not the first intake passage. Also, the compressor may be driven bya turbine included in a second exhaust passage coupled to the secondintake passage. For example, the compressed fresh intake air may bedrawn into the engine cylinder through a second intake valve of thesecond intake passage at a second intake valve timing, later than thefirst intake valve timing (e.g., the boosted fresh air may be drawn inafter the intake stroke has begun and after the first intake valve hasalready opened). The low pressure EGR (LP-EGR) and the boosted freshintake air may be mixed in the cylinder. Further, the aircharge mixturemay be mixed with fuel and combusted in the cylinder.

In this way, a stratified aircharge may be delivered to the cylinder butmay be homogeneously mixed with fuel in the cylinder prior tocombustion. By keeping the EGR out of the compressor, compressor foulingand contamination may be reduced. By not expending compressor work ondelivering EGR, turbocharger efficiency can be improved. Further, bymixing the delivered LP-EGR with the delivered boosted fresh air in thecylinder, and not before, dilution of the boosted intake air with EGR inthe intake passage may be reduced. By separating EGR delivery from boostdelivery, delays in turbocharger control as well as EGR control, inparticular during transients, can also be reduced. As such, the separateintake passages also enable the use of a smaller turbocharger to providethe desired boost without compromising boosting efficiency. Overall,engine efficiency and performance is improved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an engine including a split intakemanifold and a split exhaust manifold and associated exhaust gasrecirculation systems.

FIG. 2 shows an example embodiment of an engine cylinder of FIG. 1coupled to first and second intake passages, as well as first and secondexhaust passages.

FIG. 3 shows a partial engine view.

FIG. 4 shows a high level flow chart illustrating a routine that may beimplemented for operating the engine cylinder of FIG. 2, according tothe present disclosure.

FIG. 5 shows example cylinder intake valve and exhaust valve timings forthe engine cylinder of FIG. 2.

FIG. 6 depicts example aircharge mixtures that may be provided to thecylinder of FIG. 2 via the first and second intake passages duringdifferent operating conditions.

FIG. 7 shows a high level flowchart illustrating a routine that may beimplemented for coordinating intake air throttle operation withturbocharger operation during a tip-in event.

FIG. 8 shows a graph explaining example intake air throttle and EGRvalve adjustments during a tip-in.

FIG. 9 shows a high level flow chart illustrating a routine that may beimplemented for adjusting the operation of an EGR cooler based on engineoperating conditions.

DETAILED DESCRIPTION

The following description relates to systems and methods for controllingan engine, such as the engine system of FIGS. 1-3, by providingaircharge of differing pressure and/or differing composition (e.g.,different fresh air to EGR ratios) to an engine cylinder throughdistinct intake passages at different times in an engine cycle.Specifically, an intake aircharge at or below barometric pressure can beprovided to the cylinder separate from an intake aircharge at compressorpressure Likewise, an intake aircharge including recirculated exhaustgas can be provided to the cylinder separate from an intake airchargehaving fresh air. Still other combinations may be possible, aselaborated in FIG. 6. An engine controller may be configured to performa control routine, such as the routine of FIG. 4, to open a firstcylinder intake valve at an earlier timing than a second cylinder intakevalve (FIG. 5), thereby providing a first aircharge of a firstcomposition at a different time in the engine cycle than a secondaircharge of a second composition. The intake valve timings may befurther coordinated with corresponding exhaust valve timings (FIG. 5).The position of one or more air intake throttles and EGR valves coupledto the different intake passages may be adjusted and coordinated tocompensate for transients, as elaborated in FIGS. 7-8. Additionally, thevarious EGR valves may be adjusted to enable the intake aircharge ofeach intake passage to be heated or cooled by respective EGR coolers, aselaborated in FIG. 9. In this way, an amount of turbocharger compressionwork expended on drawing EGR may be reduced, thereby increasing theaverage intake and/or exhaust gas pressure supplied to and from theturbocharger, improving turbocharger output. Additionally, by keeping anEGR-based aircharge separate from a boost-based aircharge until they aremixed in the cylinder, both EGR control and boost control delays may bereduced. Overall, the benefits of both EGR and boosting can be extended,thereby improving engine performance and fuel economy.

FIG. 1 shows a schematic depiction of an example turbocharged enginesystem 100 including a multi-cylinder internal combustion engine 10 anda turbocharger 50. As a non-limiting example, engine system 100 can beincluded as part of a propulsion system for a passenger vehicle. Engine10 may include a plurality of cylinders 14. In the depicted example,engine 10 includes three cylinders arranged in an in-line configuration.However, in alternate examples, engine 10 can include two or morecylinders such as 4, 5, 8, 10 or more cylinders, arranged in alternateconfigurations, such as V, boxed, etc. Each cylinder 14 may beconfigured with a fuel injector 166. In the depicted example, fuelinjector 166 is a direct in-cylinder injector. However, in otherexamples, fuel injector 166 can be configured as a port based fuelinjector. Further details of a single cylinder 14 are described below inFIGS. 2-3.

Each cylinder 14 of engine 10 is configured to receive an intakeaircharge (including fresh air and/or recirculated exhaust gas) from afirst intake passage 42, as well as a second intake passage 44. As such,second intake passage 44 may be separate from, but parallel to, firstintake passage 42. First intake passage 42 may include an air intakethrottle 62 downstream of an air filter 60. The position of throttle 62can be adjusted by control system 15 via a throttle actuator (not shown)communicatively coupled to controller 12. By modulating throttle 62, anamount of fresh air may be inducted from the atmosphere into engine 10and delivered to the engine cylinders at or below barometric (oratmospheric) pressure via first intake passage 42. First intake passage42 may be split into multiple intake conduits 43 a-43 c downstream ofthrottle 62.

Each intake conduit 43 a-43 c may be coupled to a distinct enginecylinder and may be configured to deliver a portion of the intakeaircharge of intake passage 42 to the corresponding cylinder.

Second intake passage 44 may include an air intake throttle 64downstream of a charge aircooler 56 and a turbocharger compressor 52.Specifically, compressor 52 of turbocharger 50 may be included in, andcoupled to, second intake passage 44 but not to first intake passage 42.The position of throttle 64 can be adjusted by control system 15 via athrottle actuator (not shown) communicatively coupled to controller 12.By modulating air intake throttle 64, while operating compressor 52, anamount of fresh air may be inducted from the atmosphere into engine 10and delivered to the engine cylinders at compressor (or boosted)pressure via second intake passage 44. Second intake passage 44 may besplit into multiple intake conduits 45 a-45 c downstream of throttle 64.Each intake conduit 45 a-45 c may be coupled to a distinct cylinder andmay be configured to deliver a portion of the intake aircharge of intakepassage 44 to the corresponding cylinder.

Exhaust gases generated during cylinder combustion events may beexhausted from each cylinder 14 along a first exhaust passage 46 and asecond exhaust passage 48. Exhaust passage 46 may be split into multipleexhaust conduits 47 a-47 c. Specifically, each exhaust conduit 47 a-47 cmay be coupled to a distinct cylinder and may be configured to deliver aportion of exhaust gas discharged from the corresponding cylinder intoexhaust passage 46. Exhaust gas flowing through first exhaust passage 46may be treated by one or more exhaust after-treatment devices, such ascatalysts 70 and 72, before being discharged to the atmosphere alongtailpipe 35.

In the same way, second exhaust passage 48 may be split into multipleexhaust conduits 49 a-49 c. Each exhaust conduit may be coupled to adistinct cylinder and may be configured to deliver a portion of exhaustgases discharged from the corresponding cylinder to exhaust passage 48.A turbine 54 of turbocharger 50 may be included in, and coupled to,second exhaust passage 48 but not to first exhaust passage 46. Thus,products of combustion that are exhausted via exhaust passage 48 can bedirected through turbine 54 to provide mechanical work to compressor 52via a shaft (not shown). In some examples, turbine 54 may be configuredas a variable geometry turbine, wherein controller 12 may adjust theposition of the turbine impeller blades (or vanes) to vary the level ofenergy that is obtained from the exhaust gas flow and imparted tocompressor 52.

Alternatively, exhaust turbine 54 may be configured as a variable nozzleturbine, wherein controller 12 may adjust the position of the turbinenozzle to vary the level of energy that is obtained from the exhaust gasflow and imparted to compressor 52.

Exhaust gas flowing through second exhaust passage 48 may be treated byone or more exhaust after-treatment devices, such as catalyst 72, beforebeing discharged to the atmosphere along tailpipe 35. In the depictedexample, exhaust gas from second exhaust passage 48 is combined withexhaust gas from first exhaust passage 46 downstream of turbine 54 andcatalyst 70, but upstream of catalyst 72 such that the combined exhaustgas is discharged to the atmosphere along tailpipe 35. However, inalternate embodiments, exhaust passage 46 and 48 may not recombine andmay discharge exhaust gas via separate tailpipes. Exhaust passages 46and 48 may also include one or more exhaust gas sensors, as furtherelaborated in FIG. 3 Engine 10 may further include one or more exhaustgas recirculation (EGR) passages for recirculating at least a portion ofexhaust gas from first and second exhaust passages 46 and 48, to firstand second intake passages 42 and 44, respectively. Specifically, firstexhaust passage 46 may be communicatively coupled to first intakepassage 42 via a first EGR passage 80 including a first EGR cooler 82and a first EGR valve 84. An engine controller may be configured to openthe first EGR valve 84 to recirculate an amount of exhaust gas at orbelow atmospheric pressure to the first intake passage 42. In this way,low-pressure EGR (LP-EGR) may be diverted from the first exhaust passageto the first intake passage.

Likewise, second exhaust passage 48 may be communicatively coupled tosecond intake passage 44 via a second EGR passage 90 including a secondEGR cooler 92 and a second EGR valve 94. An engine controller may beconfigured to open the second EGR valve 94 to recirculate an amount ofexhaust gas, at compressor pressure, from upstream of the turbine 54 tothe second intake passage 44, downstream of the compressor 52. In thisway, high-pressure EGR (HP-EGR) may be provided to the engine via thesecond intake and exhaust passages. By providing LP-EGR through a firstEGR passage while providing HP-EGR through a second, separate EGRpassage, both HP-EGR and LP-EGR may be provided simultaneously, therebyextending the EGR benefits.

EGR coolers 82 and 92 may be configured to lower a temperature ofexhaust gas flowing through the respective EGR passages beforerecirculation into the engine intake. In an alternate embodiment, EGRcoolers 82 and 92 may be positioned at the junction of the EGR passageand the corresponding intake passage. In this position, as elaboratedherein with reference to FIG. 9, under certain conditions the EGRcooler(s) may be advantageously used to heat an intake airchargedelivered to the cylinder. Specifically, the EGR cooler may be used toprovide a heated aircharge (e.g., heated fresh air, or a mixture ofheated exhaust gas and fresh air) to the engine cylinder during someconditions, while proving a cooled aircharge (e.g., cooled EGR) to theengine cylinder during other conditions. In one example, during coldconditions, aircharge delivered to the cylinder via the second intakepassage may be heated before entering the compressor to avoid waterdroplets impinging on the compressor.

In still further embodiments, a conduit may couple the EGR passages. Theconduit may coupled the second EGR passage 90, from a position locatedbetween EGR valve 94 and EGR cooler 92, to the first EGR passage 80, ata position located between

EGR valve 84 and EGR cooler 82. Herein, during some conditions, higherpressure exhaust gas released into the second exhaust passage, via thesecond exhaust valve, may be cooled in EGR cooler 92 and the heat may betransferred to a coolant. The cooled exhaust gas may be recirculated tothe engine intake via the lower pressure first intake passage.Alternatively, the cooled exhaust gas may be exhausted to the atmospherevia first exhaust passage 46 and tailpipe 35. In this way, a largeramount of work may be extracted from the exhaust gas.

Engine system 100 may further include a valve actuator 96 for adjustingvalve operation of cylinder 14. Specifically, valve actuator 96 may beconfigured to open a first intake and/or exhaust valve of cylinder 14 ata first timing while opening a second intake and/or exhaust valve ofcylinder 14 at a second timing. In this way, a first aircharge of afirst composition at or below barometric pressure may be provided to theengine cylinder at a first timing while a second aircharge of a second,different composition at compressor pressure may be provided to theengine cylinder at a second, different timing. As a non-limitingexample, as shown in FIGS. 2-3, valve actuator 96 may be configured as acam actuator wherein the intake and/or exhaust valves of each cylinder14 are coupled to respective cams. A controller may be configured toadjust a phase (or cam profile) of valve actuator 96 (or cam actuator)based on engine operating conditions to open a first intake valve at thefirst timing to deliver the first aircharge while opening a secondintake valve at the second timing to deliver the second aircharge. Forexample, as elaborated herein in FIG. 5, intake valve timings may bestaggered to induct a portion of an intake aircharge through thecompressor while naturally aspirating the other portion of the intakeaircharge.

The controller may be further configured to adjust the valve phase toopen a first exhaust valve at a first timing while opening a secondexhaust valve at a second, different timing to release exhaust atdifferent pressures while at different positions in an engine cycle. Forexample, as elaborated herein in FIG. 5, exhaust valve timings may bestaggered to separate the release of blow down gases (e.g., expandingexhaust gases in a cylinder before time when a piston of the cylinderreaches bottom dead center expansion stroke) from the release ofresidual exhaust gases (e.g., gases that remain in the cylinder afterblow-down). In one example, by coordinating the timing of the firstintake valve with the timing of the first exhaust valve, and likewisethe timing of the second intake valve with the timing of the secondexhaust valve, exhaust energy can be transferred from the release ofblow-down gases through the turbocharger turbine in the second exhaustpassage to operate the turbocharger compressor in the second intakepassage to provide boost benefits. At the substantially same time,residual gases can be diverted from the first exhaust passage to thefirst intake passage to provide EGR benefits. In this way, the desiredEGR dilution may be provided without expending additional energy onpumping exhaust gas from the exhaust manifold to the intake manifold viaan EGR cooler, even at higher loads.

It will be appreciated that while engine system 100 is shownrecirculating exhaust gas at or below barometric pressure through thefirst intake passage, in still further embodiments, such as where thefirst intake passage is coupled to a fuel vapor recovery system of theengine, the first intake passage may be configured to recirculate one ormore of purge vapors, crankcase vapors, and gaseous or vaporized fuelvapors to the cylinder at or below barometric pressure.

Engine system 100 may be controlled at least partially by a controlsystem 15 including controller 12 and by input from a vehicle operatorvia an input device (as shown in FIG. 3). Control system 15 is shownreceiving information from a plurality of sensors 16 (various examplesof which are described herein) and sending control signals to aplurality of actuators 81. As one example, sensors 16 may include intakeair pressure and temperature sensors, MAP sensors and MAT sensors in oneor both intake passages. Other sensors may include a throttle inletpressure (TIP) sensor for estimating a throttle inlet pressure (TIP)and/or a throttle inlet temperature sensor for estimating a throttle airtemperature (TCT) coupled downstream of the throttles in each intakepassage. In other examples, one or more of the EGR passages may includepressure, temperature, and air-to-fuel ratio sensors, for determiningEGR flow characteristics. Additional system sensors and actuators areelaborated below with reference to FIG. 3. As another example, actuators81 may include fuel injector 166, EGR valves 84 and 94, valve actuator96, and throttles 62 and 64. Other actuators, such as a variety ofadditional valves and throttles, may be coupled to various locations inengine system 100. Controller 12 may receive input data from the varioussensors, process the input data, and trigger the actuators in responseto the processed input data based on instruction or code programmedtherein corresponding to one or more routines. Example control routinesare described herein with regard to FIGS. 4, 7 and 9.

Now referring to FIGS. 2-3, a single cylinder 14 of internal combustionengine 10 is shown. As such, components previously introduced in FIG. 1are represented with the same reference numbers and are notre-introduced. FIG. 2 shows a first view 200 of cylinder 14. Herein,cylinder 14 is shown with four ports including two intake ports 17 and18, and two exhaust ports 19 and 20. Specifically, first intake port 17of cylinder 14 may receive a first aircharge at or below atmosphericpressure via a first intake valve 30 from first intake conduit 43 acoupled to first intake passage 42. The first aircharge may includefresh air, recirculated exhaust gas of a lower pressure (LP-EGR) or amixture of fresh air and LP-EGR, introduced into the cylinder at orbelow atmospheric pressure. Second intake port 18 of cylinder 14 mayreceive a second aircharge at compressor pressure via a second intakevalve 31 from second intake conduit 45 a coupled to second intakepassage 44. The second aircharge may include fresh air, recirculatedexhaust gas of a higher pressure (HP-EGR) or a mixture of fresh air andHP-EGR, introduced into the cylinder at a boosted pressure after beingcompressed by compressor 52.

A portion of cylinder combustion products may be discharged from a firstexhaust port 19 of cylinder 14 via a first exhaust valve 32 into firstexhaust conduit 47 a coupled to first exhaust passage 46. Anotherportion of cylinder combustion products may be discharged from a secondexhaust port 20 of cylinder 14 via a second exhaust valve 33 into secondexhaust conduit 49 a coupled to second exhaust passage 48. Exhaust gasmay be subsequently released to the atmosphere along tailpipe 35.Specifically, the first and second exhaust passages may recombinedownstream of the turbine and upstream of emission control device 72allowing exhaust gas released into the first exhaust passage to betreated by emission control devices 70 and 72 prior to release whileallowing exhaust gas released into the second exhaust passage to betreated by device 72 prior to release along tailpipe 35. Additionally oroptionally, a portion of the exhaust gas may also be recirculated fromfirst exhaust conduit 47 a to first intake passage 43 a via first EGRpassage 80 while a portion of exhaust gas may be recirculated fromsecond exhaust conduit 49 a to first intake conduit 45 a via second EGRpassage 90. In still other embodiments, the second exhaust passage maybe configured to provide exhaust gas to the first or second intakepassage, and the first exhaust passage may be configured to provideexhaust gas to either the first or second intake passage.

In the depicted example, first intake valve 30 and second intake valve31 may each be operated by respective intake valve cams (FIG. 3). Theposition of the intake cams, and thereby the timing of the intakevalves, may be determined by an intake cam actuator 97 via camshaft rod101 Likewise, first exhaust valve 32 and second exhaust valve 33 mayeach be operated by respective exhaust cams (FIG. 3), the position ofthe exhaust cams determined by an exhaust cam actuator 98 via camshaftrod 102. However, in alternate embodiments, each intake valve and eachexhaust valve may have independent valve actuators. Further still, thefirst intake valve and the first exhaust valve may be coupled to a(common) valve actuator while the second intake valve and the secondexhaust valve are coupled to a different valve actuator. Controller 12may be configured to adjust a phase of intake valve actuator 97 based onengine operating conditions to open first intake valve 30 at a firstintake valve timing and open second intake valve 31 at a second,different intake valve timing. For example, the first timing may beadjusted relative to the second timing so as to provide a first intakeaircharge including fresh air and/or recirculated exhaust gas tocylinder 14 at a first, lower pressure earlier in the engine cycle(e.g., at an earlier part of an intake stroke) while providing a secondintake aircharge including fresh air and/or recirculated exhaust gas tocylinder 14 at a second, higher pressure later in engine cycle (e.g., ata later part of the same intake stroke in the same engine cycle).

In the same way, controller 12 may be configured to adjust a phase ofexhaust valve actuator 98 based on engine operating conditions to openfirst exhaust valve 32 and second exhaust valve 33 at specified timings.In one example, the phase of exhaust valve actuator 97 may be adjustedrelative to a phase of valve actuator 98 such that the opening and/orclosing of intake valves 30 and 31 is coordinated with (or based on) theopening and/or closing of corresponding exhaust valves 32 and 33. Forexample, the first exhaust valve may be opened to selectively exhaust(or recirculate) residual exhaust gases while second exhaust valve maybe opened to selectively exhaust blow down gases through the turbine, todrive the coupled compressor. Example first and second intake andexhaust valve timings are illustrated in FIG. 5.

Referring to FIG. 3, it shows an alternate view 300 of internalcombustion engine 10. Engine 10 is depicted with combustion chamber 14,coolant sleeve 118, and cylinder walls 136 with piston 138 positionedtherein and connected to crankshaft 140. Combustion chamber 14 is showncommunicating with intake passage 146 and exhaust passage 148 viarespective intake valves 150 and exhaust valves 156. As previouslyelaborated in FIGS. 1-2, each cylinder 14 of engine 10 may receive anintake aircharge along two intake conduits and may exhaust combustionproducts along two exhaust conduits. In the depicted view 300, intakepassage 146 and exhaust passage 148 represent the first intake conduitand first exhaust conduit leading to/from the cylinder (such as conduits43 a and 47 a of FIG. 2) while the second intake and second exhaustconduits leading to/from the cylinder are not visible in this view. Asalso previously elaborated in FIG. 2, each cylinder of engine 10 mayinclude two (or more) intake valves and two (or more) exhaust valvescoupled to the respective intake and exhaust conduits. In the depictedview 300, at least one of the intake valves is shown as an intake poppetvalve 150 and at least one of the exhaust valves is shown as an exhaustpoppet valve 156 located at an upper region of cylinder 14. Intake valve150 and exhaust valve 156 may be controlled by controller 12 usingrespective cam actuation systems including one or more cams. The camactuation systems may utilize one or more of cam profile switching(CPS), variable cam timing (VCT), variable valve timing (VVT) and/orvariable valve lift (VVL) systems to vary valve operation. In thedepicted example, each intake valve 150 is operated by an intake cam 151and each exhaust valve 156 is operated by an exhaust cam 153. Theposition of intake valve 150 and exhaust valve 156 may be determined byvalve position sensors 155 and 157, respectively. In alternativeembodiments, the intake and/or exhaust valve may be controlled byelectric valve actuation. For example, cylinder 14 may alternativelyinclude an intake valve controlled via electric valve actuation and anexhaust valve controlled via cam actuation including CPS and/or VCTsystems. In still other embodiments, the intake and exhaust valves maybe controlled by a common valve actuator or actuation system, or avariable valve timing actuator or actuation system.

In one example, intake cam 151 includes separate and different cam lobesthat provide different valve profiles (e.g., valve timing, valve lift,duration, etc.) for each of the two intake valves of combustion chamber14. Likewise, exhaust cam 153 may includes separate and different camlobes that provide different valve profiles (e.g., valve timing, valvelift, duration, etc.) for each of the two exhaust valves of combustionchamber 14. Alternatively, exhaust cam 153 may include a common lobe, orsimilar lobes, that provide a substantially similar valve profile foreach of the two exhaust valves.

For example, a first cam profile of a first intake valve of combustionchamber 14 may have a first lift amount and a first opening timing andduration. A second cam profile of a second intake valve of combustionchamber 14 may have a second lift amount and a second opening timing andduration. In one example, the first lift amount may be less than thesecond lift amount, the first opening timing may be earlier (oradvanced) than the second opening timing, and/or the first openingduration may be shorter than the second opening duration. In addition,in some examples, the phase of the first and second cam profiles may beindividually adjusted relative to the phase of the engine crankshaft.Thus, the first intake cam profile can be positioned to open the intakevalve near TDC of the intake stroke of combustion chamber 14 so that afirst intake valve can open near TDC and close near BDC of the intakestroke. On the other hand, the second intake cam profile can open asecond intake valve near BDC of the intake stroke. Thus, the timing ofthe first intake valve and the second intake valve can separate a firstintake aircharge received via a first intake passage from a secondintake aircharge received via a second, different intake passage.

In the same way, different cam profiles for the different exhaust valvescan be used to separate exhaust gases exhausted at cylinder pressurefrom exhaust gases exhausted at exhaust pressure. For example, a firstexhaust cam profile can open the first exhaust valve after BDC expansionstroke. On the other hand, a second exhaust cam profile can bepositioned to open the second exhaust valve at BDC of the expansionstroke such that the second exhaust valve can open and close before BDCexpansion stroke. Further, the second cam profile can be adjusted inresponse to engine speed to adjust exhaust valve opening and closing toselectively exhaust blow-down gas of the combustion chamber. Thus, thetiming of the first exhaust valve and the second exhaust valve canisolate cylinder blow-down gases from residual gases. While in the aboveexample the first exhaust valve timing is later in an engine cycle thanthe second exhaust valve timing, it will be appreciated than in analternate example, the first exhaust valve timing may be earlier in anengine cycle than the second exhaust valve timing. For example, duringsurge conditions, the second exhaust valve may be opened after theopening of the first exhaust valve.

By flowing a portion of the exhaust gas (e.g., higher pressure exhaust)through the turbine and a higher pressure exhaust passage, while flowingthe remaining portion of the exhaust gas (e.g., lower pressure exhaust)through catalytic devices and a lower pressure exhaust passage, the heatrecovered from the exhaust gas can be increased while improving theturbine's work efficiency. By coordinating the timing of the exhaustvalves and the timing of the intake valves, a portion of the residualexhaust gases can be delivered to provide EGR while another portiondrives the turbocharger compressor. Specifically, in one embodiment, theengine can be cleaved into a naturally-aspirated portion operating at alower pressure, and a boosted portion operating at a higher pressureproviding various synergistic benefits of EGR and boost. In addition,this configuration enables the engine to be operated with a smallerturbine and compressor while yielding lower turbo lag.

In still further embodiments, both exhaust valves may be opened at thesame time to provide a waste-gate like behavior Likewise, both intakevalves may be opened at the same time to provide a compressor-bypassvalve like behavior. As such, the advantages provided by the splitintake manifold may be availed even in the absence of a split exhaustmanifold. Further, the advantages may be provided even in the absence ofEGR passages. For example, the waste-gate like behavior andcompressor-bypass valve like behavior may be achieved whether there areone or more EGR passages, or no EGR passages between the split intakeand the split exhaust.

Exhaust gas sensor 128 is shown coupled to exhaust passage 148. Sensor128 may be positioned in the exhaust passage upstream of one or moreemission control devices, such as devices 70 and 72 of FIGS. 1-2. Sensor128 may be selected from among various suitable sensors for providing anindication of exhaust gas air/fuel ratio such as a linear oxygen sensoror UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygensensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or COsensor, for example. The downstream emission control devices may includeone or more of a three way catalyst (TWC), NOx trap, various otheremission control devices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 3shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. In an alternate embodiment,injector 166 may be a port injector providing fuel into the intake portupstream of cylinder 14.

Fuel may be delivered to fuel injector 166 from a high pressure fuelsystem 8 including fuel tanks, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12. Fueltanks in fuel system 8 may hold fuel with different fuel qualities, suchas different fuel compositions. These differences may include differentalcohol content, different octane, different heat of vaporizations,different fuel blends, and/or combinations thereof etc. In someembodiments, fuel system 8 may be coupled to a fuel vapor recoverysystem including a canister for storing refueling and diurnal fuelvapors. The fuel vapors may be purged from the canister to the enginecylinders during engine operation when purge conditions are met. Forexample, the purge vapors may be naturally aspirated into the cylindervia the first intake passage at or below barometric pressure.

Controller 12 is shown in FIG. 3 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Storage medium read-only memory110 can be programmed with computer readable data representinginstructions executable by processor 106 for performing the methods androutines described below as well as other variants that are anticipatedbut not specifically listed. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal

(PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft140; throttle position (TP) from a throttle position sensor; absolutemanifold pressure signal (MAP) from sensor 124, cylinder AFR from EGOsensor 128, and abnormal combustion from a knock sensor and a crankshaftacceleration sensor. Engine speed signal, RPM, may be generated bycontroller 12 from signal PIP. Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold.

Based on input from one or more of the above-mentioned sensors,controller 12 may adjust one or more actuators, such as fuel injector166, throttle 162, spark plug 199, intake/exhaust valves and cams, etc.The controller may receive input data from the various sensors, processthe input data, and trigger the actuators in response to the processedinput data based on instruction or code programmed therein correspondingto one or more routines. An example control routine is described hereinwith regard to FIG. 4.

Now turning to FIG. 4, an example routine 400 is shown for delivering afirst aircharge to an engine cylinder through a first intake passagewhile delivering a second aircharge to the engine cylinder through asecond, parallel but separate intake passage.

The first and second aircharges may have different compositions (e.g.,differing ratios of fresh air to recirculated exhaust gas), differentpressures (e.g., one aircharge at a higher boost pressure while theother aircharge at a lower, sub-barometric pressure), differenttemperatures (e.g., one aircharge heated to a higher temperature whilethe other aircharge is cooled to a lower temperature), etc. Further, thedifferent aircharges may be delivered at different timings so as tostagger their delivery during a given intake stroke.

At 402, engine operating conditions may be estimated and/or measured.These may include, for example, ambient temperature and pressure, enginetemperature, engine speed, crankshaft speed, transmission speed, batterystate of charge, fuels available, fuel alcohol content, catalysttemperature, driver demanded torque, etc.

At 404, based on the estimated engine operating conditions, a desired(total) aircharge may be determined. This may include determining anamount of fresh intake air, an amount of exhaust gas recirculation(EGR), and an amount of boost. Further, a ratio of fresh intake air tobe delivered at or below barometric pressure (BP) relative to freshintake air to be delivered at boost pressure may be determined.Likewise, a ratio of EGR delivered at higher pressure (HP-EGR) relativeto EGR delivered at lower pressure (LP-EGR) may be determined.

In one example, in response to a higher torque demand, the desired(total) aircharge may include a higher amount of fresh intake air and alower amount of EGR. Further, the aircharge may include a higher amountof boosted fresh intake air and a lower amount of fresh air at or belowBP. In another example, during mid-high engine load conditions, when theengine is warmed up, the desired (total) aircharge may include a higheramount of EGR and a lower amount of fresh intake air. Further, theaircharge may include a higher amount of LP-EGR and a lower amount ofHP-EGR.

Based on the desired total aircharge, the routine may further determinea first aircharge to be delivered to an engine cylinder along a firstintake passage at a first, lower pressure (such as, at or belowbarometric pressure), as well as a second aircharge to be delivered tothe cylinder along a second, separate intake passage at a second, higherpressure (such as, at a boost pressure). Specifically, the first andsecond aircharges may be mixed in the cylinder to provide the desiredtotal aircharge. The first aircharge delivered along the first intakepassage may include fresh air, recirculated exhaust gas (LP-EGR) or acombination of the two, delivered at or below barometric pressure.Likewise, the second aircharge delivered along the second intake passagemay include fresh air, recirculated exhaust gas (HP-EGR) or acombination of the two, delivered at a boost pressure, or compressorpressure. Various first and second aircharge combinations that may bedelivered to the cylinder along the first and second intake passages arefurther elaborated herein with reference to FIG. 6.

At 406, settings for the first and second EGR valves may be determinedbased on the desired aircharge. For example, based on the desiredaircharge, a first EGR valve in a first EGR passage may be opened by anamount to recirculate a first amount of exhaust gas from a first exhaustpassage to a first intake passage. Herein, the first amount of exhaustgas may be at a first, lower pressure (such as, at or below barometricpressure) to thereby provide LP-EGR. As another example, based on thedesired aircharge, a second EGR valve in a second, separate EGR passagemay be opened by an amount to recirculate a second amount of exhaust gasfrom a second, separate exhaust passage to a second, separate intakepassage. As previously elaborated, the second exhaust passage may bearranged in parallel to the first exhaust passage, the second intakepassage may be arranged in parallel to the first intake passage, and thesecond EGR passage may be arranged in parallel to the first EGR passage,even though all the passages may be separate from each other. Herein,the second amount of exhaust gas may be at a second, higher pressure(such as, at boost or compressor pressure) to thereby provide HP-EGR.Specifically, the second EGR valve may be opened to deliver the secondamount of exhaust gas from upstream of a turbocharger turbine coupled tothe second exhaust passage to downstream of a turbocharger compressorcoupled to the second intake passage.

At 408, based on the desired aircharge, a first intake valve timing fordelivering the first aircharge to the cylinder through a first intakevalve coupled to the first intake passage, and a second intake valvetiming for delivering the second aircharge to the cylinder through asecond intake valve coupled to the second intake passage, may bedetermined. In one example, where the first intake valve and the secondintake valve are coupled to an intake valve actuator, a valve phase ofthe intake valve actuator may be adjusted to open the first intake valveat the first intake valve timing and the second intake valve at thesecond intake valve timing. The first intake valve timing may beadjusted relative to the second intake valve timing based on engineoperating conditions. Specifically, the first timing may be adjusted tobe earlier in an engine cycle than the second timing. For example, aselaborated in FIG. 5, the first intake valve timing may be earlier in anintake stroke (that is, closer to intake stroke TDC) while the secondtiming may be later in the same intake stroke (that is, further fromintake stroke TDC).

In addition to first and second intake valve timings, a valve lift aswell as a duration of intake valve opening for each intake valve may bedetermined. The valve phase of the intake valve actuator may beaccordingly adjusted. In one example, the first intake valve may beopened with a first amount of valve lift while the second intake valveis opened with a second, different amount of valve lift. For example, aselaborated in FIG. 5, the first amount of valve lift of the first intakevalve may be smaller than the second amount of valve lift of the secondintake valve. In another example, the first intake valve may be openedfor a first duration while the second intake valve is opened for asecond, different duration. For example, as elaborated in FIG. 5, thefirst intake valve may be opened for a smaller duration than the secondintake valve.

In the same way, a first exhaust valve timing for a first exhaust valvecoupled to the first exhaust passage and a second exhaust valve timingfor a second exhaust valve coupled to the second exhaust passage may bedetermined. In one example, where the first exhaust valve and the secondexhaust valve are coupled to an exhaust valve actuator, a valve phase ofthe exhaust valve actuator may be adjusted to open the first exhaustvalve at the first exhaust valve timing and the second exhaust valve atthe second exhaust valve timing. The first intake valve timing and thesecond intake valve timing may be selected based on engine operatingconditions. In one example, as elaborated in FIG. 5, the first andsecond exhaust valves may be opened at a common exhaust valve timing.Alternatively, they may be staggered.

The valve phase of the intake and exhaust valve actuators may also beadjusted so as to coordinate the timing of the exhaust valve events witha timing of the intake valve events. Specifically, the first intakevalve timing of the first intake valve may be based on a first exhaustvalve timing of the first exhaust valve (e.g., the first intake valvetiming may be retarded from the first exhaust valve timing by apredetermined amount), while the second intake valve timing of thesecond intake valve may be based on a second exhaust valve timing of thesecond exhaust valve (e.g., the second intake valve timing may beretarded from the second exhaust valve timing by a predeterminedamount).

At 410, based on the desired aircharge and the engine operatingconditions, settings for air intake throttles coupled to each intakepassage may be determined. Further, fuel injector settings (e.g.,timing, amount of injection, duration of opening, etc.) as well asturbocharger settings may be determined. For example, a compressorsetting for the turbocharger coupled to the second intake passage may bedetermined based on the amount of boost desired (e.g., based on theamount of boosted aircharge desired).

At 412, based on the determined EGR valve settings, the first and secondEGR valves may be opened. Specifically, the routine includes opening afirst EGR valve in a first EGR passage to recirculate a first amount ofexhaust gas, at or below barometric pressure, from the first exhaustpassage to the first intake passage. The routine further includesopening a second EGR valve in a second EGR passage to recirculate asecond amount of exhaust gas, at compressor pressure (that is, boostpressure), from the second exhaust passage, upstream of the turbochargerturbine, to the second intake passage, downstream of the turbochargercompressor.

At 414, the routine includes opening the first intake valve of the firstintake passage at the first intake valve timing to deliver the first(unboosted) aircharge at or below barometric pressure to the cylinder.At 416, the routine includes opening the second intake valve of thesecond intake passage at the second intake valve timing to deliver thesecond (boosted) aircharge at compressor pressure to the cylinder. Assuch, providing the second boosted aircharge includes operating theturbocharger compressor, coupled to the second intake passage (and notcoupled to the first intake passage), according to the determined boostsettings.

As further elaborated with reference to FIG. 6, the first and secondaircharges may include various combinations of fresh air andrecirculated exhaust gas at varying pressures. For example, the firstaircharge being delivered to the cylinder may include a first amount offresh intake air and a first amount of recirculated exhaust gas (LP-EGR)at or below barometric pressure while the second aircharge beingdelivered to the cylinder may include a second amount of fresh intakeair and a second amount of recirculated exhaust gas (HP-EGR) at boostpressure.

At 418, the routine includes direct injecting an amount of fuel into thecylinder and mixing the first aircharge with the second aircharge andthe injected fuel in the cylinder. The mixture of the injected fuel andthe first and second aircharges may then be combusted in the cylinder.In one example, where the first intake aircharge includes recirculatedexhaust gas only and the second intake aircharge includes fresh aironly, the fresh air and the EGR may be separately delivered to thecylinder along separate intake passages, and then the aircharges may bemixed, for the first time, in the cylinder. The mixed aircharge may thenbe further mixed with injected fuel and combusted in the cylinder. Inanother example, where the first intake aircharge includes LP-EGR onlyand the second intake aircharge includes HP-EGR only, the recirculatedexhaust gases of different pressures may be separately delivered to thecylinder along the separate intake passages, and then mixed, for thefirst time, in the cylinder. Likewise, in an example where the firstintake aircharge includes fresh intake air at or below atmosphericpressure and the second intake aircharge includes boosted fresh intakeair, the fresh air of different pressures may be separately delivered tothe cylinder along the separate intake passages, and then mixed, for thefirst time, in the cylinder

In still another example, where each of the first aircharge and thesecond aircharge include at least some fresh air and at least somerecirculated exhaust gas, a first amount of LP-EGR may be mixed with afirst amount of fresh intake air at or below barometric pressure in thefirst intake passage to form the first aircharge while a second amountof HP-EGR may be mixed with a second amount of boosted fresh intake airat compressor pressure in the second intake passage to form the secondaircharge. Each aircharge may then be delivered separately to the enginecylinder and mixed, for the first time, in the cylinder rather thanearlier in the intake passage. The mixture of aircharges may then befurther mixed with injected fuel and combusted in the cylinder.

In this way, the different aircharges may be delivered separately butmixed thoroughly in the cylinder to provide a homogenized cylinderaircharge. By allowing the aircharge homogenization to occur in thecylinder, engine performance and EGR benefits may be increased. Byadjusting a first timing of the first intake valve relative to a secondtiming of the second intake valve and a timing of the first and secondexhaust valves, the different aircharges may be delivered at differenttimes but may be mixed in the cylinder to provide a homogenized finalcylinder aircharge.

Now turning to FIG. 5, map 500 depicts example intake valve timings andexhaust valve timings, with respect to a piston position, for an enginecylinder configured to receive a first intake aircharge from a firstintake passage through a first intake valve, receive a second intakeaircharge from a second, separate intake passage through a second,different intake valve, and exhaust cylinder combustion products intoeach of a first exhaust passage through a first exhaust valve, and to asecond, different exhaust passage through a second exhaust valve. Byadjusting a first timing of the first intake valve relative to a secondtiming of the second intake valve and a timing of the first and secondexhaust valves, the different aircharges may be delivered at differenttimes to provide some stratification, but may be mixed in the cylinderto provide a homogenized final cylinder aircharge.

Map 500 illustrates an engine position along the x-axis in crank angledegrees (CAD). Curve 502 depicts piston positions (along the y-axis),with reference to their location from top dead center (TDC) and/orbottom dead center (BDC), and further with reference to their locationwithin the four strokes (intake, compression, power and exhaust) of anengine cycle.

During engine operation, each cylinder typically undergoes a four strokecycle including an intake stroke, compression stroke, expansion stroke,and exhaust stroke. During the intake stroke, generally, the exhaustvalves close and intake valves open. Air is introduced into the cylindervia the corresponding intake passage, and the cylinder piston moves tothe bottom of the cylinder so as to increase the volume within thecylinder. The position at which the piston is near the bottom of thecylinder and at the end of its stroke (e.g. when the combustion chamberis at its largest volume) is typically referred to by those of skill inthe art as bottom dead center (BDC). During the compression stroke, theintake valves and exhaust valves are closed. The piston moves toward thecylinder head so as to compress the air within combustion chamber. Thepoint at which the piston is at the end of its stroke and closest to thecylinder head (e.g. when the combustion chamber is at its smallestvolume) is typically referred to by those of skill in the art as topdead center (TDC). In a process herein referred to as injection, fuel isintroduced into the combustion chamber. In a process herein referred toas ignition, the injected fuel is ignited by known ignition means, suchas a spark plug, resulting in combustion. During the expansion stroke,the expanding gases push the piston back to BDC. A crankshaft convertsthis piston movement into a rotational torque of the rotary shaft.During the exhaust stroke, exhaust valves are opened to release theresidual combusted air-fuel mixture to the corresponding exhaustpassages and the piston returns to TDC.

Curve 504 depicts a first intake valve timing, lift, and duration for afirst intake valve (Int_1) coupled to a first intake passage of theengine cylinder while curve 506 depicts a second intake valve timing,lift, and duration for a second intake valve (Int_2) coupled to a secondintake passage of the engine cylinder. Curves 508 a and 508 b depictexample exhaust valve timings, lifts, and durations for a second exhaustvalve (Exh_2) coupled to a second exhaust passage of the enginecylinder, while curves 510 a and 510 b depict example exhaust valvetimings, lifts, and durations for a first exhaust valve (Exh_1) coupledto a first exhaust passage of the engine cylinder. As previouslyelaborated, the first and second intake passages may be separate from,but arranged parallel to each other. Likewise, the first and secondexhaust passages may be separate from, but arranged parallel to eachother. Further, the first intake passage may be communicatively coupledto the first exhaust passage via a first EGR passage while the secondintake passage may be communicatively coupled to the second exhaustpassage via a second EGR passage.

In the depicted example, the first intake valve is opened at a firsttiming (curve 502) that is earlier in the engine cycle than the secondtiming (curve 504) at which the second intake valve is opened.Specifically, the first timing for the first intake valve is closer tointake stroke TDC, just before CAD2 (e.g., at or just before intakestroke TDC).

In comparison, the second timing for the second intake valve is retardedfrom intake stroke TDC, after CAD2 but before CAD3. In this way, thefirst intake valve may be opened at or before the start of an intakestroke and may be closed before the intake stroke ends, while the secondintake valve may be opened after the start of the intake stroke and mayremain open at least until a subsequent compression stroke hascommenced.

Additionally, the first intake valve may be opened at the first timingwith a first, lower amount of valve lift L1 while the second intakevalve may be opened at the second timing with a second, higher amount ofvalve lift L2. Further still, the first intake valve may be opened atthe first timing for a first, shorter duration D1 while the secondintake valve may be opened at the second timing for a second, longerduration D2.

In one example, where the first and second intake valves are coupled toan intake valve actuator, a valve phase of the actuator may be adjustedto open the first intake valve at the first timing while opening thesecond intake valve at the second timing. The valve phase of theactuator may also be adjusted to enable the first intake valve to beopened with the first amount of valve lift for the first duration whileopening the second intake valve with the second, different amount ofvalve lift for the second duration. While the depicted exampleillustrates different timing, lifts and durations for the differentintake valves, it will be appreciated that in alternate embodiments, theintake valves may have the same amount of valve lift and/or sameduration of opening while opening at staggered timings.

Now turning to the exhaust valves, curves 508 a and 510 a depict a firstexample of exhaust valve timing wherein both the first and the secondexhaust valves (Exh_1, Exh_2) are opened at a common timing, startingsubstantially at exhaust stroke BDC, at or around CAD1, and endingsubstantially at exhaust stroke TDC, at or around CAD2. Specifically, inthis example, the first and second exhaust valves may be operated withinthe exhaust stroke. Additionally, in this example, both the first andsecond exhaust valves are opened with the same amount of lift L3 and forthe same duration D3. In the depicted example, lift L3 may have a valuesmaller than lift L2 but larger than lift L1 of the intake valves. Inone example, lift L3 may have a value equal to the mean or average oflifts L1 and L2.

Curves 508 b and 510 b depict a second example of exhaust valve timingwherein the timing of the first and the second exhaust valves isstaggered. Specifically, the second exhaust valve is opened closer to(or at) power (or expansion) stroke BDC, at or just before CAD1 (e.g.,at or just before power stroke BDC), while the timing of the firstexhaust valve is retarded from power stroke BDC, after CAD1 but beforeCAD2. In this way, the second exhaust valve may be opened at or beforethe start of an exhaust stroke, just as the piston bottoms out at theend of the power stroke, and may be closed before the exhaust strokeends. In comparison, the first exhaust valve may be opened after thestart of the exhaust stroke and may remain open at least until asubsequent intake stroke has commenced. Additionally, the second exhaustvalve may be opened with a second, lower amount of valve lift L4 whilethe first exhaust valve is opened with a first, higher amount of valvelift L5. Further still, the second exhaust valve may be opened for asecond, shorter duration D4 while the first exhaust valve is opened fora first, longer duration D5. In the depicted example, the first exhaustvalve timing is later in the engine cycle than the second exhaust valvetiming. However, in an alternate embodiment, such as during surgeconditions, the first exhaust valve timing may be earlier in the enginecycle than the second exhaust valve timing.

In one example, a cam profile of the second exhaust valve can beadjusted to open and close the second exhaust valve at expansion strokeBDC and selectively exhaust blow-down gases of the cylinder into thesecond exhaust passage. On the other hand, the cam profile of the firstexhaust valve may be adjusted to open the exhaust valve after expansionstroke BDC and selectively exhaust the remaining residual gases of thecylinder into the first exhaust passage.

In one example, where the first and second exhaust valves are coupled toan exhaust valve actuator, a valve phase of the actuator may be adjustedto open the first exhaust valve at the first timing while opening thesecond exhaust valve at the second (same or different) timing. The valvephase of the actuator may also be adjusted to enable the first exhaustvalve to be opened with the first amount of valve lift and for the firstduration while opening the second intake valve with the second (same ofdifferent) amount of valve lift and for the second (same or different)duration. For example, the valve phase of the intake valve actuator maybe adjusted based on the valve phase of the exhaust valve actuator toenable a staggered intake valve timing (as shown in curves 504, 506) tobe coordinated with a staggered exhaust valve timing (as shown in curves508 b, 510 b). Additionally, an amount of overlap between the intakevalve timings and the exhaust valve timings may be adjusted to adjustthe amount of EGR provided to the cylinder. In still further examples,both exhaust valves may be opened at the same time to provide awaste-gate like behavior Likewise, both intake valves may be opened atthe same time to provide a compressor-bypass valve like behavior. In thesame way, an amount of valve overlap between the exhaust valves may beadjusted based on the desired wastegating, and the amount of valveoverlap between the intake valves may be adjusted based on the desiredcompressor bypassing.

In this way, using different exhaust valve timings, engine efficiencycan be increased while engine emissions are reduced by separatingexhaust gases released at higher pressure (e.g., expanding blow-downexhaust gases in a cylinder before time when a piston of the cylinderreaches bottom dead center expansion stroke) from exhaust gases releasedat lower pressure (e.g., residual exhaust gases that remain in thecylinder after blow-down) into the different exhaust passages. Inparticular, exhaust energy can be transferred from the blow-down gasesto one of two exhaust passages to operate a turbocharger turbine (whichin turn drives a turbocharger compressor) or provide EGR at a higherpressure. At the substantially same time, residual gases may be directedto the other exhaust of the two exhaust passages to heat a catalyst,thereby reducing engine emissions, or to provide EGR at a lowerpressure. In this way, exhaust gases can be used more efficiently thansimply directing all the exhaust gas of a cylinder through a single,common exhaust port to a turbocharger turbine. As such, severaladvantages may be achieved. For example, the average exhaust gaspressure supplied to the turbocharger can be increased to improveturbocharger output. Additionally, fuel economy may be improved andparticulate emissions may be reduced by decreasing an engine warm-uptime. Further, the method can reduce engine emissions since at least aportion of cylinder exhaust gases are directly routed from the cylinderto the catalyst.

Various examples of intake aircharges delivered to the cylinder throughthe first and second intake passages is now elaborated with reference toFIG. 6. Specifically, table 600 lists example combinations of a firstaircharge that is delivered to the cylinder along a first intake passagethrough a first intake valve at a first, earlier intake valve timing,and a second aircharge that is delivered to the cylinder along a second,separate intake passage through a second, separate intake valve at asecond, later intake valve timing. As such, the first and secondaircharges may be delivered separately and then mixed (for the firsttime) in the cylinder with each other and with direct injected fuelprior to combustion of the mixture.

In one example, during a first condition (Cond_1), the first intakeaircharge delivered along the first intake passage may include freshintake air that is naturally aspirated at or below barometric pressure.At the same time, the second intake aircharge may include boosted freshintake air that is delivered at compressor pressure along the secondintake passage. Herein, by providing naturally aspirated fresh intakeair and boosted fresh intake air through separate intake passages to theengine cylinder, the naturally-aspirated portion of the intake airchargecan be inducted without investing the work of compression (of theturbocharger) while only the boosted portion of the intake airchargeneeds to be compressed. In this way, a thermal efficiency gain isadvantageously achieved.

In another example, during a second condition (Cond_2), the first intakeaircharge provided along the first intake passage may include at leastsome recirculated exhaust gas at or below barometric pressure. That is,low pressure-EGR may be recirculated from the first exhaust passage tothe first intake passage. At the same time, the second intake airchargemay include boosted fresh intake air that is delivered at compressorpressure along the second intake passage.

Herein, by providing low-pressure EGR and boosted fresh intake airthrough separate intake passages, LP-EGR may be kept out of thecompressed air path. This provides multiple benefits. First, compressionwork of the turbocharger is not expended on delivering the EGR. As aresult, turbocharger compression efficiency is improved. Second, bykeeping LP-EGR away from the turbocharger compressor, issues related tocompressor fouling and contamination with EGR are reduced. Third, sincethe boosted fresh intake aircharge is not diluted with EGR, atemperature benefit is achieved in that the charge air cooler is notrequired to be operated to reduce a temperature of the intake aircharge.Fourth, by separating the boosted intake aircharge from the EGR basedintake aircharge, both boost control and EGR control delays can bereduced, providing synergistic benefits. Finally, by dividing the totalaircharge into a portion delivered through the naturally-aspiratedintake passage (that is, a portion that is not boosted) and a portionthat is delivered through the compressor, the compression work requiredof the compressor is reduced, providing a thermodynamic efficiencyadvantage. As such, this may enable the same compression to be providedby a smaller turbocharger (having a smaller compressor and/or turbine)without compromising on boosting efficiency and while reducingturbo-lag.

As another example, during a third condition (Cond_3), the first intakeaircharge delivered along the first intake passage may include a mixtureof recirculated exhaust gas and fresh intake air that is naturallyaspirated at or below barometric pressure. Thus, a first amount ofLP-EGR may be mixed with a first amount of fresh intake air at or belowBP and delivered to the cylinder via the first intake passage. At thesame time, the second intake aircharge may include fresh intake air atcompressor pressure. Herein, as with the previous example (duringCond_2), by providing at least some EGR via an intake passage that isseparate from the intake passage including the compressor, compressorfouling can be reduced, turbocharger and EGR control delays can bereduced, turbocharger efficiency can be improved, and boost and EGRbenefits can be extended over a wider engine operating range.

In still another example, during a fourth condition (Cond_4), the firstintake aircharge delivered along the first intake passage may include atleast some recirculated exhaust gas at or below barometric pressure. Atthe same time, the second intake aircharge may include at least somerecirculated exhaust gas at compressor pressure. That is, LP-EGR may beprovided through the first intake passage while HP-EGR is providedthrough the second intake passage. Herein, by providing LP-EGR andHP-EGR through separate intake passages to the engine cylinder, thebenefits of exhaust gas recirculation can be extended to a wider rangeof engine speed/load conditions. Additionally, HP-EGR and LP-EGR may beindependently controlled.

In another example, during a fifth condition (Cond_5), the first intakeaircharge delivered along the first intake passage may include freshintake air that is naturally aspirated at or below barometric pressure.At the same time, the second intake aircharge may include at least somerecirculated exhaust gas at compressor pressure. That is, highpressure-EGR (HP-EGR) may be recirculated from the second exhaustpassage, upstream of the turbocharger turbine, to the second intakepassage, downstream of the turbocharger compressor. Herein, by providingnaturally aspirated fresh intake air and boosted EGR through separateintake passages to the engine cylinder, intake air dilution with EGR canbe reduced.

In yet another example, during a sixth condition (Cond_6), the firstintake aircharge delivered along the first intake passage may include amixture of recirculated exhaust gas and fresh intake air that isnaturally aspirated at or below barometric pressure. At the same time,the second intake aircharge may include at least some recirculatedexhaust gas at compressor pressure. Thus, a first amount of LP-EGR maybe mixed with a first amount of fresh intake air at or below BP anddelivered to the cylinder via the first intake passage, while HP-EGR isdelivered to the cylinder via the second intake passage. Herein, as withthe previous example (Cond_4), by providing LP-EGR and HP-EGR viaseparate intake passages, the benefits of exhaust gas recirculation canbe extended to a wider range of engine speed/load conditions.

As a further example, during a seventh condition (Cond_7), the firstintake aircharge delivered along the first intake passage may include atleast some recirculated exhaust gas at or below barometric pressure. Atthe same time, the second intake aircharge may include a mixture ofrecirculated exhaust gas and fresh intake air at compressor pressure.Thus, a second amount of HP-EGR may be mixed with a second amount offresh intake air at compressor pressure and delivered to the cylindervia the second intake passage, while LP-EGR is delivered to the cylindervia the first intake passage. Herein, as with the previous examples(Cond_4, and Cond_6), by providing HP-EGR and LP-EGR via separate intakepassages, the benefits of exhaust gas recirculation can be extended to awider range of engine speed/load conditions.

As yet another example, during an eighth condition (Cond_8), the firstintake aircharge delivered along the first intake passage may include amixture of recirculated exhaust gas and fresh air that is naturallyaspirated at or below barometric pressure. At the same time, the secondintake aircharge may include a mixture of recirculated exhaust gas andfresh intake air at compressor pressure. Thus, a first amount of LP-EGRmay be mixed with a first amount of fresh intake air at or below BP anddelivered to the cylinder via the first intake passage while a secondamount of HP-EGR may be mixed with a second amount of fresh intake airat compressor pressure and delivered to the cylinder via the secondintake passage. Herein, by providing a first aircharge at a first, lowerpressure to the cylinder separate from a second aircharge at a second,higher pressure to the cylinder via distinct intake passages, EGR andboost may be used over a wide range of operating conditions whileallowing each to be better controlled.

As another example, during a ninth condition (Cond_9), the first intakeaircharge delivered along the first intake passage may include freshintake air that is naturally aspirated at or below barometric pressure.At the same time, the second intake aircharge may include a mixture ofrecirculated exhaust gas and at least some fresh intake air atcompressor pressure. Thus, a second amount of HP-EGR may be mixed with asecond amount of fresh intake air at compressor pressure and deliveredto the cylinder via the second intake passage, while naturally aspiratedfresh intake is delivered to the cylinder via the first intake passage.Herein, by providing a boosted intake aircharge and a naturallyaspirated intake aircharge via separate intake passages, the naturallyaspirated intake aircharge can be inducted without investing the work ofcompression while expending the turbocharger's compression work only onthe boosted intake aircharge.

Now turning to FIG. 7, an example routine 700 is described for reducingturbo-lag. Specifically, the routine depicts coordinating the intake airthrottle operation of a first intake passage with turbocharger operationin a second intake passage during a tip-in event to reduce turbo-lag. Byreducing turbo-lag, turbocharger efficiency can be increased and engineperformance can be improved. FIG. 8 illustrates an example throttle-EGRvalve adjustment during a tip-in, as per the routine of FIG. 7, by wayof map 800.

At 702, the routine includes confirming a tip-in event. In one example,a tip-in event may be confirmed in response to a driver tipping in (orpressing) the accelerator pedal beyond a threshold position. In anotherexample, a tip-in event may be confirmed in response to a driver torquedemand being higher than a threshold.

As such, prior to the tip-in event, each engine cylinder may have beenreceiving an amount of recirculated exhaust gas (specifically, LP-EGR)through a first intake passage while receiving fresh intake air througha second, separate but parallel intake passage. Exhaust gas may havebeen recirculated at a lower pressure from a first exhaust passagecommunicatively coupled to the first intake passage, downstream of anfirst air intake throttle, via a first EGR passage including a first EGRvalve. In response to a tip-in event, at 704, the routine includesincreasing an amount of fresh intake air while decreasing the amount ofrecirculated exhaust gas delivered to the cylinder via the first intakepassage. Specifically, the routine includes opening (or increasing anopening of) the first air intake throttle in the first intake passage toincrease the amount of fresh intake air inducted into the cylinderthrough the first intake passage, while closing (or decreasing anopening of) the first EGR valve in the first EGR passage coupled betweenthe first intake passage and the first exhaust passage to decrease theamount of exhaust gas recirculated through the first intake passage.

While adjusting the air intake throttle and EGR valve in the firstintake passage, at 706, the routine further includes, operating aturbocharger compressor coupled to the second intake passage to increasean amount of boosted fresh intake air delivered to the cylinder via thesecond intake passage for a duration of the tip-in. Specifically, theengine controller may initiate operation of the turbocharger compressorwhile opening (or increasing an opening of) a second air intake throttlecoupled in the second intake passage, downstream of the compressor, toincrease an amount of boosted fresh intake air delivered to thecylinder. The controller may also close (or decrease an opening of) asecond EGR valve included in a second EGR passage coupled between thesecond intake passage and the second exhaust passage to decrease anamount of higher pressure exhaust gas recirculated through the secondintake passage. In one example, the first air intake throttle may begradually opened and the first EGR valve may be gradually closed with aprofile based on the compressor's speed profile. The adjustments to thefirst and second air intake throttles and first and second EGR valvesmay be continued for a duration corresponding to a duration until thecompressor attains a threshold speed. In one example, the thresholdspeed may correspond to a speed beyond which turbo-lag may be reduced,such as a speed at which the pressure output of the compressor isgreater than the atmospheric (or barometric) pressure under the givenengine operating conditions.

At 708, it may be confirmed whether the compressor speed has reached thethreshold speed. Alternatively, it may be determined if thepredetermined duration corresponding to a duration until the compressorattains the threshold speed has elapsed (e.g., using a timer). If not,then at 710, the routine may maintain the first intake air throttle openand the first EGR valve closed while operating the compressor. Incomparison, if the compressor speed has reached the threshold speed, orif the predetermined duration has elapsed, then at 712, after theduration has elapsed, the routine includes decreasing the amount offresh intake air while increasing the amount of recirculated exhaust gasdelivered to the cylinder via the first intake passage. Specifically,the routine includes closing (or decreasing an opening of) the first airintake throttle in the first intake passage, to decrease the amount offresh intake air inducted into the cylinder through the first intakepassage, while opening (or increasing an opening of) the first EGR valvein the first EGR passage coupled between the first intake passage andthe first exhaust passage to increase the amount of exhaust gasrecirculated through the first intake passage. In one example, the firstair intake throttle may be gradually closed and the first EGR valve maybe gradually opened with a profile based on the engine speed profile.

In this way, the cylinder may be filled with fresh intake air via thefirst intake passage while the compressor is brought up to speed in thesecond intake passage so that by the time the compressor is at thedesired boost speed, the cylinder may already be filled with freshintake air. In other words, by the time the compressor is at boostpressure, boosted fresh intake air may be provided to the cylinder viathe second intake passage while additional fresh air is provided to thecylinder via the first intake passage. Consequently, turbo-lag caused bywaiting for a compressor to come to speed before boosted fresh air canbe inducted into the cylinder is reduced. Then, when the compressor hasreached the desired speed, EGR can be phased in through the first andsecond intake passages (specifically, LP-EGR via the first intakepassage and HP-EGR via the second intake passage) to provide EGRbenefits in addition to boost benefits. By reducing turbo-lag,turbocharger efficiency is improved and engine performance is increased.By providing boost and EGR benefits together, synergistic improvementsin engine performance can be achieved.

The steps of FIG. 7 are further clarified by the example of FIG. 8. Map800 depicts an engine torque output at graph 802 over a duration ofengine operation. Corresponding changes in a turbocharger compressorspeed are depicted at graph 804. Changes in the position of a first airintake throttle and a first EGR valve coupled to the first air intakepassage are shown at graphs 810 and 812, respectively, while changes inthe position of a second air intake throttle and a second EGR valvecoupled to the second air intake passage are shown at graphs 806 and808, respectively. As such, only the second intake passage may includethe turbocharger compressor. Changes in the composition of a firstaircharge (Air_Int_1) delivered to the cylinder through the first intakepassage, resulting from adjustments to the first EGR valve and throttle,are shown at graphs 818 and 820 while changes in the composition of asecond aircharge (Air_Int_2) delivered to the cylinder through thesecond intake passage, resulting from adjustments to the second EGRvalve and throttle, are shown at graphs 814 and 816. Changes in the netcylinder aircharge (Cyl_aircharge) are shown at graphs 822 and 824,respectively. In each of graph 814-824, the solid line represents afresh air component of the aircharge while the dashed line represents anEGR component of the aircharge.

Prior to t1, based on engine operating conditions, a lower torque may bedemanded. Herein, the net cylinder aircharge corresponding to the lowertorque output may include a relatively higher amount of EGR (dashed lineof graph 824) and a relatively smaller amount of fresh air (solid lineof graph 822). By using EGR during low load conditions, fuel economy andreduced emissions benefits may be achieved. The net cylinder airchargedelivered to the cylinder prior to t1 may be provided by mixing a firstintake aircharge delivered along the first intake passage with a secondintake aircharge delivered along the second intake passage.Specifically, the first intake aircharge may include a higher amount ofrecirculated exhaust gas (graph 820) at or below barometric pressure(that is, LP-EGR) and a lower amount of naturally aspirated fresh air(graph 818) provided by opening the first EGR valve (graph 812) and thesecond intake throttle (graph 810) by corresponding amounts. Incomparison, the second intake aircharge may include fresh intake air(solid line of graph 814) and substantially no EGR (dashed line of graph816) provided by opening the second intake throttle (graph 806) whileclosing the second EGR valve (graph 808).

At t1, a tip-in event may occur leading to a higher torque demand. Forexample, the higher torque output may be demanded in response to avehicle operator pressing the accelerator pedal to beyond a thresholdposition. In response to the tip-in event, the compressor (graph 804)may be operated to provide a boosted intake aircharge, while the secondintake throttle (graph 806) is opened (e.g., fully opened) to inductboosted fresh air into the cylinder. However, the boosted aircharge maynot be available until the compressor reaches a threshold speed leadingto a turbo lag. To reduce the turbo lag, while the compressor isspinning up in the second intake passage, the first intake airchargedelivered along the first intake passage may be temporarily adjusted toincrease the portion of fresh intake air while reducing the portion ofEGR (graphs 808-820). Specifically, the first EGR valve (graph 812) maybe closed while the first intake throttle (graph 810) is fully opened toincrease the amount of naturally aspirated fresh air inducted into thecylinder while reducing the amount of LP-EGR delivered to the cylinder.

At t2, when the compressor is at or above the desired threshold speed, aboosted fresh intake aircharge may be delivered to the cylinder alongthe second intake passage (graph 814). At this time, the amount of freshair delivered along the first intake passage may be decreased bygradually closing the first intake throttle (graph 810), while LP-EGRmay be gradually returned by opening the first EGR valve (graph 812). Inthis way, while the compressor spins up in one intake passage, fresh aircan be inducted into the cylinder through the other intake passage todilute out any EGR already present in the cylinder. Consequently, whenthe compressor has spun-up, the inducted fresh air in the second intakepassage can be compressed to meet the higher torque demand. Further,when the compressor has spun-up, the compressor may be used to inductboosted fresh air through one intake passage while LP-EGR is deliveredin parallel to the engine cylinder through the other intake passage. Inthis way, turbo lag can be reduced while providing EGR benefitsalongside boost benefits.

It will be appreciated that in still other embodiments, turbo lag may beadditionally or optionally reduced by closing EGR valves, deactivatingthe first exhaust valve and fully opening second exhaust valve. Then, ifEGR is desired, one or more of the EGR valves may be opened to providethe desired EGR, as elaborated above at 808 and 812.

Now turning to FIG. 9, an example routine 900 is shown for adjusting theoperation of an EGR cooler based on engine operating conditions.Specifically, the routine enables an EGR cooler positioned at thejunction of an EGR passage and an intake passage (e.g., at the junctionof the first EGR passage and the first intake passage) to be used tocool an intake aircharge delivered to the cylinder (e.g., via the firstintake passage) during some conditions while enabling the EGR cooler toheat the intake aircharge during other conditions.

At 902, engine operating conditions may be estimated and/or measured.These may include, for example, ambient temperature and pressure, enginetemperature, engine speed, crankshaft speed, transmission speed, batterystate of charge, fuels available, fuel alcohol content, catalysttemperature, driver demanded torque, etc. At 904, it may be determinedwhether intake aircharge heating is desired. In one example, intakeaircharge heating may be desired when the engine is not knock-limited.For example, if no knocking is anticipated, the intake aircharge may beheated to lower the engine pumping work and improve fuel economy.

If heating is requested, then at 906, heating conditions may beconfirmed. Specifically, it may determined whether all conditions arepresent for being able to operate the EGR cooler as a heater to heat anintake aircharge. For example, where the EGR cooler is a liquid coolantbased cooler, it may be confirmed that the coolant temperature is higherthan the intake air temperature. Further, it may be confirmed thatknocking conditions are not present (that is, knock is not occurring oranticipated). If all the heating conditions are met, then at 908, theroutine includes closing the first EGR valve while opening the firstintake throttle in the first intake passage to heat the intake airchargeinducted into the cylinder along the first intake passage using thefirst EGR cooler. In this way, the intake aircharge delivered along thefirst intake passage can be heated before being inducted into thecylinder, thereby reducing engine pumping losses and improving engineefficiency. As such, if any or all of the heating conditions are notmet, then the controller may determine that the EGR cooler cannot beoperated as an aircharge heater at this time, and the routine may end.

If intake aircharge heating is not required at 904, then at 910 it maybe determined whether intake aircharge cooling is required. In oneexample, cooling may be used to reduce the temperature of EGR beingdelivered to the cylinder. The cooled EGR may reduce cylinder knockwhile also providing fuel economy and NOx reduction benefits. If nocooling is desired, the routine may end. If cooling is desired, then at912, cooling conditions may be confirmed. Specifically, it may bedetermined whether all the conditions are present for being able tooperate the EGR cooler to cool an intake aircharge. For example, it maybe confirmed that the cooling will not lead to condensation on thecompressor. If all the cooling conditions are met, then at 914, theroutine includes opening the second EGR valve while closing the secondintake throttle in the second intake passage to cool the EGR in theintake aircharge inducted into the cylinder along the second intakepassage using the second EGR cooler. Additionally, or optionally, theroutine may include opening the first EGR valve while closing the firstintake throttle in the first intake passage to cool the EGR in theintake aircharge inducted into the cylinder along the first intakepassage using the first EGR cooler. In this way, the intake airchargecan be cooled before being inducted into the cylinder, and temperaturecontrol of EGR may be achieved. As such, if any or all of the coolingconditions are not met, then the controller may determine that the EGRcooler cannot be operated as an aircharge cooler at this time, and theroutine may end.

In one example, intake aircharge heating may include heating only theEGR delivered to the cylinder. For example, when the EGR cooler ispositioned within the recirculation passage (or EGR passage), asdepicted in FIGS. 1-2, the EGR valve may be opened and the EGR coolermay be operated as a heater to heat the EGR and mix the heated EGR withcooler fresh intake air in the intake passage before delivery to thecylinder. Alternatively, if the EGR cooler is positioned at the junctionof the EGR passage and the intake passage, intake aircharge heating mayinclude heating the fresh intake air and/or the EGR delivered to thecylinder. For example, the EGR valve may be closed while the EGR cooleris operated as a heater to heat the fresh intake air before delivery tothe cylinder. Alternatively, the EGR valve may be opened and the EGRcooler may be operated as a heater to heat the fresh air and the EGR,the heated EGR and heated fresh air being mixed in the intake passageprior to delivery to the cylinder.

In still other examples, one of the EGR coolers may be operated as acooler while the other EGR cooler is operated as a heater. For example,during a first condition, an engine controller may operate the first EGRcooler in the first intake passage to heat a first amount of exhaust gasbefore recirculating the exhaust gas to the first intake passage, andduring a second condition, the controller may operate the first EGRcooler in the first intake passage to cool the first amount of exhaustgas before recirculating the exhaust gas to the first intake passage. Atthe same time, during the first condition, the engine controller mayoperate a second EGR cooler in the second intake passage to cool asecond amount of exhaust gas before recirculating the exhaust gas to thesecond intake passage, while during the second condition, the controllermay operate the second EGR cooler in the second intake passage to heatthe second amount of exhaust gas before recirculating the exhaust gas tothe second intake passage. As such, the second EGR cooler may be used asa heater only when the compressor is not operating and no boost in beingprovided.

Further still, operation of the EGR coolers may be coordinated with theoperation of a charge air cooler positioned downstream of a turbochargercompressor (such as charge air cooler 56 of FIGS. 1-2). For example, thefirst EGR cooler in the first intake passage may be used as a heater toprovide a heated intake aircharge (including fresh intake air and/orLP-EGR) to the cylinder via the first intake passage. At the same time,the compressor in the second intake passage may be operated to provide aboosted intake aircharge while the charge air cooler downstream of thecompressor is operated to cool the boosted intake aircharge. In thisway, heated naturally aspirated air (at or below atmospheric pressure)and cooled boosted air can be provided to the cylinder simultaneously.The heated and cooled aircharges can then be mixed and combusted in thecylinder. Herein, by combining and combusting heated and cooledaircharges delivered separately but simultaneously to a cylinder, asubstantially constant compression temperature may be achieved overvarying loads, improving engine performance.

In this way, a split engine intake may be combined with a split engineexhaust to deliver different aircharges of differing composition andpressure to a cylinder at different timings. Specifically, a naturallyaspirated aircharge may be inducted separate from a boosted aircharge toreduce the amount of compression work required. By reducing the amountof work required by the compressor, an engine boosting efficiency can beincreased, even with the use of a smaller turbocharger. In anotherembodiment, EGR may be delivered separate from a boosted fresh intakeaircharge. By keeping EGR out of the compressor, fouling andcontamination of the compressor can be reduced while enabling EGRcontrol delays and turbocharger control delays to be reduced. In anotherembodiment, HP-EGR and LP-EGR may be delivered via separate passages.Herein, overall EGR control can be improved while allowing the EGRbenefits to be extended over a wider range of conditions. Additionally,over-dilution of air with EGR, in particular, when switching from a highcylinder air charge to a low cylinder aircharge, can be reduced byenabling a second path of non-dilute air to be provided. Overall, EGRand boost efficiency can be improved to increase engine performance.

Note that the example control and estimation routines included hereincan be used with various system configurations. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations, orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted Likewise, the order of processing isnot necessarily required to achieve the features and advantages of theexample embodiments described herein, but is provided for ease ofillustration and description. One or more of the illustrated actions,functions, or operations may be repeatedly performed depending on theparticular strategy being used. Further, the described operations,functions, and/or acts may graphically represent code to be programmedinto computer readable storage medium in the control system

Further still, it should be understood that the systems and methodsdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are contemplated. Accordingly, the presentdisclosure includes all novel and non-obvious combinations of thevarious systems and methods disclosed herein, as well as any and allequivalents thereof.

1. A method of operating a boosted engine, comprising: drawing at leastsome recirculated exhaust gas at or below barometric pressure from oneof two exhaust passages into an engine cylinder through a first intakepassage; and drawing at least some fresh air at compressor pressure intothe cylinder through a second, separate intake passage coupled to theother of the two exhaust passages.
 2. The method of claim 1, wherein thefirst intake passage is arranged parallel to the second intake passage.3. The method of claim 1, wherein the one of the two exhaust passages isa first exhaust passage, and wherein drawing at least some recirculatedexhaust gas includes drawing an amount of exhaust gas from the firstexhaust passage via a first exhaust valve, and delivering them into thefirst intake passage via a first intake valve.
 4. The method of claim 3,wherein the other of two exhaust passages is a second, separate exhaustpassage that is arranged in parallel to the first exhaust passage. 5.The method of claim 4, wherein drawing at least some fresh air atcompressor pressure includes operating a turbocharger compressor coupledto the second intake passage and not the first intake passage to draw anamount of compressed fresh air, the turbocharger compressor driven by aturbocharger turbine coupled to the second exhaust passage and not thefirst exhaust passage.
 6. The method of claim 5, further comprising,mixing the recirculated exhaust gas at or below barometric pressure withthe fresh air at compressor pressure in the cylinder.
 7. The method ofclaim 6, further comprising, delivering fuel to the mixture ofrecirculated exhaust gas and fresh air in the cylinder and combustingthe mixture in the cylinder.
 8. The method of claim 7 wherein drawingrecirculated exhaust gas at or below barometric pressure includesopening the first intake valve coupled to the first intake passage at afirst intake valve timing, and wherein drawing fresh air at compressorpressure includes opening a second intake valve coupled to the secondintake passage at a second, different intake valve timing.
 9. The methodof claim 8, wherein the first and second intake valves are coupled to anintake valve actuator, further comprising, adjusting a valve phase ofthe intake valve actuator to open the first valve at the first intakevalve timing and the second valve at the second intake valve timing. 10.The method of claim 9, wherein drawing recirculated exhaust gas at orbelow barometric pressure further includes adjusting an exhaust valveactuator to open the first exhaust valve coupled to the first exhaustpassage at a first exhaust valve timing, and wherein drawing fresh airat compressor pressure includes adjusting the exhaust valve actuator toopen a second exhaust valve coupled to the second exhaust passage at asecond, different exhaust valve timing.
 11. The method of claim 10,wherein the first intake valve timing is earlier in an engine cycle thanthe second intake valve timing.
 12. The method of claim 10, wherein thefirst exhaust valve timing is later in an engine cycle than the secondexhaust valve timing.
 13. A method of reducing turbocharger lag,comprising: in response to a tip-in, increasing an amount of intake airand decreasing an amount of recirculated exhaust gas delivered to acylinder via a first intake passage while operating a compressor coupledto a second, different intake passage to increase an amount of boostedintake air delivered to the cylinder via the second intake passage for aduration since the tip-in.
 14. The method of claim 13, wherein theincreasing an amount of intake air and decreasing an amount ofrecirculated exhaust gas includes opening a first intake throttle in thefirst intake passage while closing a first EGR valve in a first EGRpassage coupled between a first exhaust passage and the first intakepassage.
 15. The method of claim 14, wherein the duration includes aduration until the compressor attains a threshold speed.
 16. The methodof claim 15, further comprising, after the duration has elapsed,decreasing the amount of intake air while increasing the amount ofrecirculated exhaust gas delivered to the cylinder via the first intakepassage.
 17. An engine system, comprising: an engine cylinder; a directinjector configured to directly inject an amount of fuel into thecylinder; a first intake passage communicatively coupled to a firstexhaust passage, the first intake passage including a first intake valvefor delivering an amount of recirculated exhaust gas to the cylinder; asecond, separate intake passage communicatively coupled to a second,separate exhaust passage, the second intake passage including a secondintake valve for delivering an amount of compressed fresh air to thecylinder; a turbocharger compressor coupled to the second intakepassage, the compressor driven by a turbine coupled to the secondexhaust passage; and a valve actuator configured to open the firstintake valve at a first intake valve timing and the second intake valveat a second, different intake valve timing.
 18. The system of claim 17,further comprising, a controller with computer readable instructions foradjusting a valve phase of the actuator to open the first intake valveat the first intake valve timing and the second intake valve at thesecond intake valve timing.
 19. The system of claim 17, wherein thefirst intake valve timing is earlier in an engine cycle intake strokethan the second intake valve timing.
 20. The system of claim 17, whereinthe first exhaust passage includes a first exhaust valve and the secondexhaust passage includes a second exhaust valve, and wherein thecontroller includes further instructions for adjusting the first intakevalve timing based on a first exhaust valve timing of the first exhaustvalve and for adjusting the second intake valve timing based on a secondexhaust valve timing of the second exhaust valve.